A study (4,164 infants) was carried out in Holland to examine the associations of duration of exclusive breastfeeding with infections in the upper respiratory (URTI), lower respiratory (LRTI), and gastrointestinal tracts (GI) in infancy. The study was part of a population-based prospective cohort study from fetal life onward in the Netherlands – the Generation R Study. The study analysed breastfeeding rates in the first six months in the following categories: never; partial for <4 months, not thereafter; partial for 4–6 months; exclusive for 4 months, not thereafter; exclusive for 4 months, partial thereafter; and exclusive for 6 months) and infections in the URTI, LRTI, and GI which were reviewed by a doctor until the age of 12 months.

The researchers found that compared with never-breastfed infants, those who were breastfed exclusively until the age of 4 months and partially thereafter had lower risks of infections in the URTI, LRTI, and GI until the age of 6 months and of LRTI infections between the ages of 7 and 12 months. Similar tendencies were observed for infants who were exclusively breastfed for 6 months or longer. Partial breastfeeding, even for 6 months, did not result in significantly lower risks of these infections. The researchers conclude that exclusive breastfeeding until the age of 4 months, and partially thereafter, was associated with a significant reduction of respiratory and gastrointestinal morbidity in infants and state that these findings support health policy strategies to promote exclusive breastfeeding for at least 4 months, but preferably 6 months, in industrialized countries.